This invention relates to a video tracker usable by the military to obtain visual location of a moving target, either friendly or enemy; the target can be any bounded object of sufficient size and contrast, such as an aircraft, a ground vehicle, a missile, or ballistic projectile. When used to track an enemy missile or projectile the video tracker functions as a defensive mechanism for enabling the military commander to fire a projectile at the target, to throw up a protective mechanism (e.g. smoke), or to change the speed or direction of his vehicle. When used to track a friendly target (projectile or missile) the video tracker functions to control the commander's missile or gun, or to inform the commander of the hit/miss distance from the enemy objective.
An aim of the video tracker is to quantitatively detect target lock-on point changes occurring from one video frame to the next. The tracker is designed to separately detect changes on the X--X (azimuth) and Y--Y (elevation) axes, to thereby provide separate readouts for controlling the turret and gun on a military vehicle (the camera platform).
Another aim of the video tracker camera optical system is to maintain the target image as a fixed percentage of the video field of view over a substantial variation in target range, e.g. from 200 meters to 2500 meters. The target image is kept sufficiently large in the tracking window (field of view) that changes in the target lock-on point are properly detectable by the camera scanning system. At the same time the target image is not so large as to overfill the tracking window, with consequent loss of target outline necessary for lock-on point detection.
Another aim of the invention is to provide circuitry for adaptively thresholding the contrast between the target image and its background, thus providing increased assurance that the camera will follow a precise target lock-on point in spite of light level changes and background scene changes occurring in the course of the tracking operation.